Metal sheets used in industry to create different shaped pieces by means of pressing, stamping or forming, for example, are provided in the form of coils. These must be uncoiled in order for the metal sheet to be handled and when this is done the sheet features undulations and distortions that are detrimental to its subsequent treatment or handling. In order to solve this drawback the sheet to be unrolled must be handled by a straightening machine where most of the stresses are eliminated. These straightening machines generally comprise a plurality of rollers between which the sheet passes.
This process is suitable for cases in which the sheets comprise a limited thickness. If the thickness exceeds a certain value, the rollers required to eliminate the stresses are very large, making the elimination of stresses in this way difficult. In these cases a drawing machine is used and by means of which the sheet is drawn to eliminate the stresses. This method can also be used for sheets of limited thickness. U.S. Pat. No. 4,751,838 discloses a drawing machine having a first moving head that holds the metal sheet and which is mounted to the floor, and a second moving head that also holds the metal sheet but which moves in relation to the first head by means of actuation means, moving away from the first head. As a result, the sheet is drawn with undulations in it being removed.
In many cases the length of the metal sheet to be drawn varies. As a result of which there are known machines that include means for moving the second head in relation to the first head prior to the drawing operation. As a result, the second head can be positioned in different start positions in relation to the first head, which enables sheets of different lengths to be drawn.
European Patent Application published as EP1923150A1 discloses a drawing machine of this type. The machine structure comprises serrated means and the actuation means comprises connection means that cooperate with the serrated means, so that when they move in relation to the first head they can be fixed in the required position, with the second head moving in conjunction with the actuation means.